Production of siloxanes



Patented Nov. 22, .1949

UNITED, sures PATENT orrics,

PRODUCTION OF 'SILOXAN ES J ames Franklinflyde and William Herbert Daudin Corning; N-m Y;,..assignors: to Corning, Glass Works, Coming, N. Y., a.-.corporation. of New York No Drawing Application February 21, 1946,"- Sri'al No. 649,385

three silicon atoms in which chain- -the terminalw silicon atoms carry three organo radicals each and the intermediate silicon atoms carry two organo radica-lseach. Molecules of this type are not subject to further condensation except through the loss of" organo radicalsfrom the" silicon. For thisreason siloxanes' ofthis char-g acter are verystablef The physical=propertiesof" thesematerials; such as viscosity and boilingpoint, are dependentupon the organora'di'cals which are bonded to-the silicon, and upon the:

number of silicon atoms per molecule:-

An object of the'present-inVentiom-is to-pro--= vide improved methods for the preparationon siloxanes of the character indicated.

In accordance with the present invention a diorganosiloxane, i. e., a siloxane containingtwo organo radicalslinked to'each'silicon by carbon to silicon bond, is reacted with 'a hexaorganmdisiloxane in the presence" of analk'ali metal hydroxide. In order to obtain copolymers'bythis interaction; rearrangement of the-silicon oxygen bond isnecessary, since the hexaorganodisiloxane is completely'condensed; and is; therefore, not

subject to further condensation either with itself or with any other siloxane;

The process hereof" is generalin' application and may be appliedinconnection with a' Wide" Both" the di'organosilox'anevariety of siloxanes; and" the hexaorganodisiloxane may'c'arry a wide range of organo radicals. The present invention is applicable in instances where the organ'o radi cals are alkyl radicals containing between 1' and 18 carbon atoms per alkyl; aryl radicalssuch as phenyl, totyl, and xenyl;.aralkyl radicalssuch. asbenzyl; alicylic radicals such as cyclohexyl-land. methylcyclopentyl; an dalkenyl radicals suchias; The reactants employed in. the present process may containvarious organo: radicals, asinthe end blocking 0t dimethyl sub-. with dimethylphenylsiloxy; This wide latitude in: the application of.

allyl an methallyl.

stituted groups. this process is due to the organo radicalsibeing; non-reactive portions of the molecules this. process, the reaction involving; the silicon-oxygen bonds only.

siloxanes- The hexaorganodisiloxanes here involved are, those materials also known as organosilicon- The (1101?!" gano substituted. siloxanes employed have ade. gree of substitution between 2 and 2.1 andmay' ethers and as triorganosilicyl oxides.

either-be: linear diorganosiloxanes or cyclic diorganosiloxanes. In the case of the linear .dior

ganosiloxanes, triorganosilicon. groups may be present at some terminal positions.

The average degree of. substitution of. the; reaction mixturewill to a substantial. extent be.

controlling, with any particular type. of organic substituents, of the physical stateof the product. The present process is effective at an averagedegree of substitution between. 2-and. 2.5 or

gano radicals per siliconnatomi The lowerthe w degree ofsubstitution, the higher will. be the molecular aggregation of the products obtained.- Light oils are obtained atthe higher degrees of. substitutionqwhentthe. organo substituents: are primarily loweralkyls. When theaveragedegree of substitutionof the: reaction mixture exceedst. 2,5}. relatively light oils-are obtained, togetherwith :the disiloxane which. is. in. excess of that sufficient to give the light-oil obtained. In such an instance, it is. generally desirable to separate. the excess disiloxane following interaction oflthe materials.

The alkalimetal hydroxide which is'employed.

ispreferably sodium or potassium hydroxid'e',.due

to the commercial availability'ofthese materials; Otheradequatelystrongjalkalis, such as thequa:

ternary ammonium. hydroxides, may be em:

ployedy Thefunction oftlie alkali in the presentprocess is to cause the. silicon to oxygen bonds. It has been found thatthe alkali metal hydroxides efiectuate' this 2.0-

to function ionically.

. 3 tion over a wide range of proportions. Thus, the silicon-oxygen bonds have been found to function ionically in the presence of as small amounts of alkali as 7000 atoms of silicon per atom of alkali metal, and also when the alkali metal hydroxide is present in amount in excess of the atomic equivalent of silicon present. Whereas the ionic action of these bonds is obtained over a wide range, in order to cause the interaction with which this invention deals, the alkali should be present in amount less than equivalent to the diorgano-substituted silicon present. It is preferred when the degree of substitution is between 2 and 2.5 that the alkali to total silicon ratio be less than the degree of substitution minus 2. In the range between this value and an amount of alkali equivalent to the diorgano substituted silicon separation of some organosilicon salt from the intercondensate frequently occurs. When the degree of substitution exceeds 2.5, the alkali should be less than equivalent to the diorgano-silicon material present.

Water is generally present in the system during the interaction. Thus, when a siloxane reacts with an alkali metal hydroxide to form a silanol and an organosilicon salt, water may be produced by condensation of the silanol. Also, the diorgano-substituted siloxane may carry hydroxyl groups, which may be eliminated from the interacting molecules during the process. It is further possible to add the alkali metal hydroxide as aqueous solution, which introduces more water into the system. In order to eflect rapid interaction, it is preferred that extraneous water (that not derived from hydroxyl groups in the diorganosiloxane and in the alkali metal hydroxide) introduced into the system be in amount not greater than 1.5 times the amount of alkali metal hydroxide, by weight. When the alkali metal hydroxide is added as aqueous solution, it is preferred that the concentration be at least 40 per cent by weight, or if less, that water be removed from the system during the course of interaction to this extent.

Inorder to accelerate initiation of the interaction, it is frequently desirable to add a polar or non-polar solvent such as, alcohol, dioxan, or benzene. While the initial accelerating effect of the solvent is obtained with a small amount of solvent, the desired interaction is obtained in the presence likewise of relatively large amounts.

The interaction hereof may be effected over a wide range of temperature from below room temperature to elevated temperature. The main difference effected by change of temperature is variation in the rate of reaction. When temperatures sufficiently elevated to cause cleavage of organo radicals are employed, the average degree of substitution is decreased, whereby the molecular complexity of the molecules produced is increased, with accompanying changes in the physical properties of the products. By such means it is possible to obtain gels and resins from a reaction mixture which has a degree of substitution above 2, and which would normally yield an oil.

Following interaction in accordance with the process hereof, it is desirable to eliminate the alkali either by neutralization, by washing with water, or by distillation in the case of low boiling oils. Removal of the alkali is desirable in order to stabilize the products and thereby prevent further rearrangement, due to shifting equilibria, depending upon the conditions to which the products is subjected.

For a better understanding of this invention, reference may be had to the following examples which should be considered only as illustrative of the method hereof.

Example 1 To 1 volume of a mixture containing 1 part by weight of hexamethyldisiloxane and 5 parts by Weight of dimethylsiloxane there were added 8 volumes of 95% ethyl alcohol containing two thirds part by weight of potassium hydroxide. The mixture was refluxed at atmospheric pressure for 10 minutes, poured into water, acidified, and collected from the aqueous mixture with ether. The ether solution was washed with water. The ether solution was freed from volatile materials, including any residual unreacted hexamethyldisiloxane together with the solvent and water by heating at 100-140 at 18 mm. pressure while passing a stream of hydrogen through the mixture. The initial dimethylsiloxane was a fluid having a viscosity of 475 cs. at C. The product had a viscosity of 82 cs. at 25 C., and increased to only cs. after being heated 15 hours at -135 C. By analysis the product contained 80.2 per cent SiOz (calculated SiOz for (CH3) 2SiO, and the reaction mixture as prepared are respectively 74%; 81.02%; and 79.8).

Example 2 To 1 volume of a mixture containing 1 part by weight of symmetrical tetramethyldiphenyldisiioxane and 3 parts of dimethylsiloxane there were added 3 volumes of 95% ethyl alcohol containing two-thirds part of potassium hydroxide. This mixture was refluxed at atmospheric pressure for 5 minutes. The reaction product was recovered as in Example 1. The dimethylsiloxane fluid employed was the same as in Example 1. The product had a viscosity of 36 cs. at 25 C. which increased to only 39 cs. after heating 15 hours at l30-135 C.

Example 3 19 parts by weight of hexamethyldisiloxane was added to a mixture of 432 parts of a highly condensed dimethylsiloxane fluid having a viscosity of 15,000 cs. and 5.1 parts of sodium hydroxide. The mixture was held at 150-160 C. for 21 hours. The mixture was then carbonated to precipitate the alkali as sodium carbonate. The reaction product was found to be substantially free of low boiling distillate, indicating that the hexamethyldisiloxane had been consumed. The product had a viscosity of 245 cs.

Example 4 A mixture of 105.1 parts by weight of octamethylcyclotetrasiloxane, 38.3 parts of hexamethyldisiloxane and 2.10 parts of KOI-I (assay 87%). The mixture was refluxed for 16.5 hours, during which time the pot temperature increased from 127 to 180 C. due to interaction of the disiloxane to form higher boiling materials. The reaction product was filtered to remove solids, neutralized, washed with water, and dried over sodium sulfate. The dried liquid had a viscosity of 4.7 cs. as compared with 2.3 and 0.65 for the reactants, respectively. A portion thereof was heated for one hour at to C. to remove traces of water and any residual hexamethyldisiloxane. The total weight loss was only 4.8% which indicated that the disiloxane had interacted. The viscosity of the reaction product, thus freed of light ends, was 5.1 cs. Upon analysis this product was found to contain 37.41% silicon. The remainder of the dried liquid was fractionally distilled whereby a series of low viscosity fluids was obtained, which fluids had the properties noted:

viscositg Fraction in cs Boiling Range 100-180 at 746.7 mini. 177-181 at 746.7 mm. 90-127 at 5 mm 122-183 at 3 mm 183-200 at 3 mm 153-205 at 0.5 mm Still pot residue in which n is a positive integer. The boiling point of compounds of this type is dependent upon the specific value of "02.

When it is desired to produce materials such as fractions da'nd '7, the other materials may be retreated with a'lkali or added to a fresh charge of reactants. Likewise the lower boiling fjend blocked fluids may be produced by interacting the higher boiling fluids with hexaorganodisiloxane, either alone or in mixture with a fresh charge of reactants.

We claim:

1. The method of preparing siloxanes which comprises interacting hexamethyldisiloxane and a cyclic dimethylsiloxane in intimate contact with an alkali metal hydroxide.

2. The method of preparing siloxanes, which comprises interacting a hexaorganodisiloxane and a diorgano siloxane, the organic radicals of said siloxanes being selected from the group consisting of alkyl and monocyclicaryl radicals, in intimate contact with an alkali metal hydroxide.

3. The method of preparing siloxanes, which comprises interacting a hexaorganodisiloxane and a diorgano siloxane, the organic radicals of said siloxanes being selected from the group consisting of alkyl and monocyclicaryl radicals, in intimate contact with an alkali metal hydroxide, the alkali metal hydroxide being present in amount less than 1 atom of alkali metal per diorgano substituted silicon atom.

4. The method of preparing siloxanes, which comprises interacting a hexaorganodisiloxane and a diorgano siloxane, the organic radicals of said siloxanes being selected from the group consisting of alkyl and monocyclicaryl radicals, in

intimate contact with an alkali metal hydroxide, in which reaction mixture the degree of substitution is between 2 and 2.5, the atomic ratio of alkali metal to silicon being less than the degree of substitution minus 2.

5. The method of preparing siloxanes, which comprises interacting a hexaorganodisiloxane and a diorgano siloxane, the organic radicals of said siloxanes being selected from the group consisting of alkyl and monocyclicaryl radicals in intimate contact with an alkali metal hydroxide, the atomic ratio of the alkali metal to silicon being less than the degree of substitution minus 2 and the alkali metal hydroxide being present in amount less than 1 atom of alkali metal per diorgano substituted silicon atom, and in the presence of water in amount less than 1.5 times the amount of alkali metal hydroxide present by weight, which water is derived from sources extraneous to said alkali metal hydroxide and said siloxanes.

6. The method of preparing siloxanes, which comprises interacting a siloxane which contains diorgano substituted silicon and which has a degree of substitution of between 2 and 2.1,. and a hexaorganodisiloxane, the organic radicals of said siloxanes being selected from the'g'roup consisting of alkyl and monocyclicaryl radicals, in intimate contact with an alkali metal hydroxide, the alkali metal hydroxide being present in amount less than 1 alkali metal atom per diorgano substituted silicon atom.

JAMES FRANKLIN HYDE. WILLIAM HERBERT DAUDT.

REFERENCES CITED The following references are of record. in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Kipping et al., J. Chem. Soc. (London), (1914), pp. 484-500.

Meads et al., J. Chem. Soc. (London), 105 (1914), pp. 679-690.

Hyde et al., J. Amer. Chem. Soc., 63 (1941), pp. 1194-1196.

Certificate of Correction Patent No. 2,489,138 November 22, 1949 JAMES FRANKLIN HYDE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 2, for totyl read tolyl; line 4, for an dalkenyl read and allcenyl; line 5, for the words an methallyl read and methall'yl; column 4, line 29, for 79.8). read 79.8%).; column 5, line 21, for [i(OH ),O] read [SflC'H hO];

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 16th day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Conuniasioner of Patents. 

